Method of inhibiting discoloration of color photographic layers containing dye images and resulting photographic products



United States Patent METHOD OF INHIBITING DISCOLORATION OF COLOR PHOTOGRAPHIC LAYERS CONTAINING DYE IMAGES AND RESULTING PHOTOGRAPH- IC PRODUCTS Roy Arthur Jelfreys, Harrow, England, assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Apr. 23. 1963, Ser. No. 274,952

Claims. (Cl. 96-55) This application is a continuation-in-part of our application Serial No. 788,053, filed January 21, 1959, now U.S. Patent No. 3,095,302.

This invention relates to color photography and more particularly to methods for preventing discoloration of photographic layers containing dye images. The invention also includes photographic layers or elements stabilized against discoloration according to the new methods.

The system of three-color photography suggested by Fischer in U.S Patent 1,055,155 issued March 4, 1913 forms the basis for certain color photographic processes and products. In one embodiment this process involves the incorporation of different color-forming coupler compounds in each of three superposed differently color-sensitizecl silver halide emulsion layers. Each of the three couplers is capable of producing a color complementary to the sensitivity of the layer in which it is incorporated by reaction with the oxidation products of certain types of photographic developing agents. In this way a developed silver image and a colored dye image are formed simultaneously in each of the three superposed emulsion layers. The silver images and residual undeveloped silver halide may then be removed from the multilayer photographic element by bleaching, fixing and washing according to now well-known methods. Alternatively, the color-forming couplers may be incorporated in the developer rather than in the emulsion layers as disclosed in Fischer U.S. Patent 1,102,028 issued June 30, 1914.

The couplers suggested by Fischer contain phenolic hydroxyl or ketomethylene groups capable of reacting with the oxidation products of aromatic amino developing agents during photographic development to form indophenol, indamine, indoaniline or azomethine (including quinone-imine) dyes. Dyes produced by developing with aminophenols in the presence of a phenol or naphthol coupler are indophenol dyes, those produced by developing with a phenylene diarnine type developer in the presence of an aniline coupler, phenol or naphthol couplers or reactive methylene compounds are indarnine, indoan-iline and azomethine dyes, respectively. Azomethine and 'indoaniline dyes are present in many of the processed photographic color products produced by current photographic processes.

While the process of Fischer U.S. Patent 1,055,155 in which the color-forming couplers are incorporated in the emulsion layers is theoretically feasible it has not been entirely successful due to the tendency of the couplers to diffuse out of their respective emulsion layers during coating or processing. For this reason it has been proposed to react the coupler molecules with high molecular weight or colloidal bodies to render the couplers non-diffusing in gelatin or other colloidal media. It has also been proposed to mix the couplers with a water-insoluble colloid such as a natural or synthetic resin or a cellulose ester and to subsequently disperse this mixture in the gelatin emulsion. Methods of this type are disclosed in Martinez U.S. Patent 2,269,158, issued January 6, 1942 and in Mannes and Godowsky U.S. Patents 2,3 04,939 and 2,304,-

ods of this type are disclosed in Jelley et al. U.S. Patent 2,322,027 issued June 15, 1943, Fierke et al. U.S. Patent 2,801,171 issued July 30, 1957 and in Porter et al. U.S. Patent 2,369,489 issued February 13, 1945 as well as in numerous other patents.

Specific couplers useful in photographic color processes in which the couplers are not dispersed in a water-immiscible solvent are disclosed in the following representative references: Mannes and Godowsky U.S. Patent 2,039,- 730 issued May 5, 1936, hydroxy diphenol couplers which form blue or blue-green dyes; Mannes and Godowsky U.S. Patent 2,108,602 issued February 15, 1938, acet-oacetamides and cyanoacetamides, containing reactive methylene groups, which form yellow dyes; Mannes and Godowsky U.S. Patent 2,115,394 issued April 26, 1938, organic compounds containing the cyanoacetyl group which form red and magnet dyes; and Richey and Jensen U.S. patent application Serial No. 670,900 filed July 10, 1957, and now abandoned, water-soluble cyan, magenta and yellow dye-forming couplers.

The developing agents useful for color development of emulsion layers containing couplers of the type described above or for the development of emulsion layers in the presence of these couplers include the well-known primary aromatic amino silver halide developing agents such as the phenylenediamines including the alkyl phenylenediamines and alkyl toluene diamines. These developing agents are usually used in the salt form such as the hydrochloride or sulfate which is more stable than the amine. The p-aminophenols and their substitution products may also be used where the amino group is unsubstituted. The N- alkyl sulfoamido alkyl-p-phenylenediamine agents of Weissberger U.S. Patent 2,193,015 issued March 12, 1940 are also very useful. All of the developing agents have an unsubstituted amino group which enables the oxidation product of the developer to couple with the color-forming compounds to form a dye image.

Many indophenol, indamine, indoaniline and azomethine dyes are relatively unstable to light with the result that dye images in finished commercial color pictures have a tendency to fade, especially when subjected to intense illumination for extended periods of time. This is true whether the source of illumination is sunlight or tungsten or fluorescent lamps. The cyan dyes are generally relatively less susceptible to fading than the other dyes commonly used in color photography. In processes in which the couplers are incorporated in the emulsion layers or in plain gelatin layers in the film, further difficulty is caused by residual unused coupler which tends to print out under the influence of light especially in the high light areas of the picture. Magenta dye-forming couplers are generally more susceptible to print-out than others.

The nearest solution to the problem of fading of dye images and print-out of residual coupler in photographic layers would be to use only couplers and dyes which are inherently stable to light. This is seldom feasible, however, since the number of couplers and dyes suitable for use in commercial photographic color processes is somewhat limited and it is often the case that the mosst suitable materials are not as stable as might be desired. Therefore, the most satisfactory approach to the fading and printout problem has been to choose couplers and dyes suitable for the particular photographic process and then attempt to protect these compounds against the usually deleterious effects of light.

In general, two methods have been suggested to prevent discoloration of photographic layers. One of these comprises overcoating the photographic layer to be protected with a substance capable of absorbing ultraviolet light. Methods of this type are disclosed in Salminen and Allen U.S. Patent 2,632,701 issued March 24, 1953 and Edgerton and Staud U.S. Patent 2,747,996 issued May 29, 1956. The other method referred to above comprises treatment of photographic layers containing dye images with certain chemical compounds particularly organic reducing agents or antioxidants, in order to stabilize the dye images and any residual coupler in the photographic layer. Methods of this type are disclosed in Vittum U.S. Patent 2,384,658, issued September 11, 1955 and Mackey U.S. Patent 2,579,435 issued December 18, 1951. Methods of the latter type have been found to be entirely empirical. For example, although the reducing agents of the Vittum patent are useful others of similar reducing properties have no effect on the stability of photographic dye images. Further, many reducing compounds which might suggest themselves as stabilizing agents not only have no stabilizing properties but actually cause stain or destruction of dye images in photographic layers. It has, therefore, been difficult to find compounds having appreciable dye stabilizing or anti-print-out properties which are also free from other undesirable characteristics. Therefore, although the above and other methods have been suggested in the art for protecting colored photographic elements against discoloration due to fading or print-out, none has .proven to he a complete solution to the problem and the search for new methods has continued.

It is an object of the present invention to provide improved methods for preventing the discoloration of photographic layers containing dye images subject to fading or print-out under the influence of light. It is a further object of the invention to provide color photographic materials including films, transparencies and prints stabilized against discoloration under the influence of light. Other objects will become apparent from the following description of the invention.

The methods of the present invention for preventing the discoloration of water permeable photographic layers containing dye images comprise treating such layers with aqueous solutions of certain organic compounds in order to introduce sufficient quantities of these treating agents into the photographic layers to inhibit fading of the dye images or print-out of any residual dye-forming coupler therein. In practice, the photographic element or layer containing the dye image, but substantially free from developed silver, silver halide and other soluble salts, is immersed in a bath comprising an aqueous solution of one of the treating agents of the invention. The photographic layer is allowed to remain in the bath until it has absorbed suflicient treating solution to inhibit discoloration. The photographic layer is then removed from the bath and allowed to dry containing the absorbed treating agent. Optionally, surplus treating solution may be removed from the surface of the photographic element or layer by means of a squeegee, rapid water rinse or other suitable means prior to drying. When a water rinse is em- .ployed, however, care must be taken not to remove absorbed treating agents from the treated layer.

As noted above, the dye images in the photographic layers to be treated according to the invention are formed by color development of latent silver halide images in the presence of color-forming coupler compounds by means of a primary aromatic amino developing agent. The dye images formed in this way may be composed of indophenol, indamine, 'azomethine or indoaniline dyes. The azomethine and indoaniline types are currently produced in many color photographic processes and the methods of the present invention are especially suitable for the stabilization of these dyes against fading and of the corresponding couplers against print-out. The developed silver image and undeveloped silver halide present 'in the photographic layer after color development are removed by conventional methods prior to treatment according to the invention.

methyl, ethyl, etc.), hydroxyl, aryl, e.g., phenyl, 0-, mand p-tolyl, etc. Especially useful amino acids of our invention include those containing from 2 to 4 carbon atoms, as well as dipeptides of these acids. Particularly useful amino acids include glycine, u-alkylglycines, tx-hydroxyalkylglycines, N-hyd-roxyalkylglycines, u-alanine, ,B-alanine, sarcosine, N, N-dimethylglycine, N,N-diethylglycine, betaine, serine, etc., as well as dipeptides of these acids, such as glycylglycine.

The term alkyl as employed herein is intended to include alkyl groups of such size that they do not render the treating agents too insoluble in water to achieve a solution concentration within the range required by the present invention, i.e., from about 2.5 to about 15 by weight. Of the alkyl substituted compounds, those containing lower alkyl groups having from 1 to about 6 carbonat-oms are most useful in the present invention; those containing methyl, ethyl and propyl groups being especially suitable.

Treating agentsto be useful in the present invention should not, of course, be capable of causing discoloration of photographic layers containing dye images or destruction of such dye images under the conditions of use. It is sometimes desirable to employ these amino acids in the form of a buffered solution so that the pH is near neutrality, i.e., between about 6 and 8. Any of the common buffering agents known in the art can be use-d, although it is apparent that many of the amino acids useful in our invention have useful buffering action of their own.

The concentration of treating agent in the aqueous treating solutions of the invention may range from a lower operable limit below which insuflicient treating agent is absorbed by the treated photographic layer to provide an appreciable increase in the stability of any dye image or residual coupler therein to an upper limit above which treating agent tends to crystallize out of the solution on the surface of the treated layer. Subject to these limits, most useful treating solutions contain from about 2.5 to about 15% of treating agent by weight. The optimum concentration of the treating solution varies with the particular treating agent employed and with the particular dyes and couplers treated as well as other factors. In general, concentrations of treating agent from about 7.5 to 10% are preferred in most cases. It should also be recognized that the nature of the photographic layer will have an effect upon the optimum concentration. For example, porous photographic elements such as photographic paper, as opposed to film, require larger amounts of treating agent for the same degree of stabilization.

The temperature at which the treatments are carried out is not critical; it being preferred, as a matter of convenience, to employ the treating solutions at room tem perature. It is, of course, important that the temperature of the treating solution should not be high enough to damage the photographic layer or element being treated or to decompose or otherwise adversely effect the treating agent.

The treating time required in the present invention varies with the permeability to the treating solution of the photographic elements being treated. In general, about 10 minutes immersion in the treating bath is sufficient in most cases although shorter or longer times may often be employed with success. It is, of course, essential that the photographic element be immersed long enough to absorb sufiicient treating agent to provide a significant improvement in the stability of the color element against discoloration.

The following examples will serve to illustrate our invention, although they should not be interpreted to limit the activity thereof. The concentrations of treating solutions are expressed in terms of precent by weight of the aqueous treating solution.

Example 1 A processed water-permeable, full-color transparency, containing magenta, cyan and yellow dye images (produced by a reversal color process) composed of indoaniline and azomethine dyes formed by color development and substantially free from developed silver and residual silver halide was immersed in a aqueous solution of glycine at room temperature for about 10 minutes. At the end of this time the transparency containing absorbed treating solution was removed from the bath and surplus liquid was removed from the surface with a squeegee. Rapid water washing of the transparency prior to squeegeeing is optional. The transparency was then allowed to dry containing absorbed glycine.

When the dry transparency was exposed to intense tungsten illumination in a fadometer for an extended period of time it was found that the above treatment enhanced the stability of the colored images in the transparency in comparison with the stability of the images in similar untreated transparencies.

The procedure of the above example was repeated substituting other aliphatic amino acids and dipeptides for the glycine treating agent. Additional treatments were also conducted in the manner described above employing the aliphatic amino acid and dipeptide treating agents in the treatment of color prints both of the negative-positive and reversal types as well as in the treatment of transparencies in which the dye images were produced by couplers incorporated in the emulsion layers as dispersions in water-immiscible solvents, e.g., as disclosed in US. Patents 2,269,158; 2,304,939; 2,304,940; 2,322,027; 2,801,- 171 and 2,369,489 referred to above. It was found that all of the treating agents improve the stability of colored dye images in the several types of photographic color materials in varying degrees. On the basis of these treatments, the preferred treating agents are glycine, glycylglycine and N-hydroxymethylglycine.

In Example 1 above, the full color transparencies em ployed were of the type described in Mannes and Godowsky US. Patents 2,039,730; 2,108,602; 2,115,394 and Richey et al. British Patent 891,158, in which the dyeforming couplers were incorporated in the developing so lutions, rather than being incorporated in the photographic element in the form of a dispersion in a water-immiscible solvent. Of course, our invention is also useful in stabilizing photographic elements containing couplers of the latter type.

In a manner similar to that described in Example 1 above, processed photographic color images carried on a paper support can also be stabilized, although it is sometimes desirable to increase the concentration of the treating agent since there may be absorption of the treating solution by the paper support. Of course, this absorption is quite harmless from the photographic quality standpoint.

Example 2 In a manner similar to that described above, a conventional photographic print on a paper support was treated for a few minutes at room temperature in a 5% aqueous solution of N,N-diethylglycine. After such treatment by immersion in the aqueous solution, the surface was squeegeed, dried, sprayed quickly with water and then dried. The treated sample, together with an untreated sample, was exposed for 240 hours to a Xenon arc. The red, green and blue density of the prints were then measured at a neutral density of 1.0. Under these conditions, the control containing no treating agent showed a blue density loss of .36, while the treated sample had a blue density loss of only about .28. The red and green density losses were about equal in both cases, although there was some improvement in this regard in the treated sample. Upon exposure for only 120 hours to the Xenon arc, there was again considerable improvement in the case of the blue density (read at neutral density 1.0), the figures being .19 for the untreated sample and only .14 for the treated sample.

Example 3 A processed three-color transparency of the type described in Example 1 was divided into three equal parts and one part was bathed in a 3.5 aqueous solution of glycine while a second portion was bathed in a 7.5 aqueous solution of N-hydroxymethylglycine. The third sample was merely washed with water. The three samples were then squeegeed dry and with a fourth sample of the same transparency serving as a control, each was exposed in a fadometer equipped with tungsten illumination for a period of hours. The following density losses, ex-

A reversal color print comprising a paper support and developed and coupled dye images was treated with water, glycine or N-hydroxymethylglycine according to the method described in Example 1. The dye images in the silver halide emulsion layers were obtained by conventional color development using positive printing paper, the emulsions of which contained conventional color-coupling compounds. The treated samples were compared with a sample of paper which had not been immersed in a water wash or treated with amino acid. The samples were then squeegeed dry and exposed to sunlight for 20,000 lumen hours per square foot. The following results were obtained:

Percentage Density Loss Treatment Cyan Magenta Yellow Nil 3 15 51 Water Wash 7 23 53 10% Glycine 5 10 37 10% N-hydroxymethylglycine 4 10 35 The amino acids of our invention can be frequently employed in the form of their water-soluble salts, such as sodium, potassium, etc., although it may sometimes be desirable to buffer such solutions in cases where the pH becomes too strongly alkaline. Such buffering treatments are, of course, well understood by those skilled in the art. It may sometimes be desirable to also include a sequestering agent in the treating solution in order to remove undesired salts, such as those of calcium and magnesium which have a tendency to form curds or scum in the water and thus produce unsightly prints where hard water is employed. Aminopolycarboxylic acids and water-soluble salts thereof are convenient sequestering agents for such use.

The treating solutions of our invention can be employed in treatment of a wide variety of colored materials, including those produced by conventional color development as described above, or they can be used to stabilize color prints produced by diffusion color techniques as described in a number of US. and foreign patents, See, for example, Land, U. S. Patents 2,559,643, issued July 10, 1951, and 2,698,798, issued January 4, 1955. Other patents describing the production of color prints by diffusion transfer techniques include Belgian 554,933 and 554, 934, both granted August 12, 1957. See also Belgian 578,470, granted November 6, 1959.

As noted above, the treatments of the present invention are applied to photographic elements or layers which contain dye images but are substantially free from developed silver or residual silver halide. The methods by which the developedsilver image formed on color development and any residual silver halide are removed from color photographic elements are well known in the art. One method commonly employed is initiated by bleaching the silver image with a solution of potassium terricyanide and potassium bromide. After this treatment the photographic element is fixed with sodium thiosulfate solution and finally washed with water to remove the soluble salts.

.A method of this type is described in Mannes, Godowsky and Wilder, US. Patent 2,252,718, issued August 19, 1941.

In practicing the methods of the present invention, it may be found, for example, that when a three color multilayer photographic transparency, film or print containing difierent typesof dyes is treated, the treatment may prove more effective for one or more of the dyes than for the remainder. As noted above, cyan dyes are normally relatively stable and, therefore, the improvement in their stability will not ordinarily be as marked as for other dyes. Similarly, inasmuch as magenta dye-forming couplers are particularly susceptible to print-out, the improvement in the stabilization of these materials will generally be greater than for other couplers.

As noted above, it is important in the present invention that significant quantities of the treating agents remain in the finished color photographic element in order to insure the desired stabilization of dye images and residual coupler against fading and print-out, respectively.

It should be understood that the present invention has been described with reference to the color processes, couplers and developing agents disclosed in representative US. patents and patent applications for purposes of illustration only and that other photographic color processes, sensitized color elements, couplers and developers may also be employed as will be obvious to those skilled in the art and that for this reason the invention is to be taken as limited only by the scope of the appended claims.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. The method of inhibiting the discoloration of a water-permeable photographic layer containing a color image, said layer being substantially free of developed silver and residual silver halide, which comprises imbibing in said layer an aqueous solution of an amino acid selected from the class consisting of glycine, B-alanine, betaine, an alkylglycine in which the alkyl group has from 1 to 6 carbon atoms, and dipeptides of the said acids.

2. The method of inhibiting the discoloration of a water-permeable photographic layer containing an image composed of a dye selected from the class consisting of azomethine, indoaniline, indophenol, and indamine dyes, said layer being substantially free of developed silver and residual silver halide, which comprises imbibing in said layer an aqueous solution of an amino acid selected from the class consisting of glycine, fi-alanine, betaine, an alkylglycine in which the alkyl group has from 1 to 6 carbon atoms, and dipeptides of the said acids.

3. The method of claim 2 in which amino acid is glycine.

4. The method of claim 2 in which the amino acid is glycylglycine.

5. The method of claim 2 in which the amino acid is N,N-diethylglycine.

6. The method of inhibiting the discoloration of a water-permeable photographic layer containing a dye image, said layer being substantially free of developed silver and residual silver halide, which comprises imbibing in said layer a substantially neutral aqueous solution of a water-soluble salt of an amino acid selected from the class consisting of glycine, fi-alanine, betaine, an alkylglycine in which the alkyl group has from 1 to 6 carbon atoms, and dipeptides of the said acids.

7. As an article of manufacture, a photographic color element having at least one developed and fixed photographic layer containing a dye image, said layer being substantially free of developed silver and residual silver halide and having incorporated therein an amino acid selected from the class consisting of glycine, fl-alanine, betaine, an alkylglycine in which the alkyl group has from 1 to 6 carbon atoms, and dipeptides of said acids, said amino acid being incorporated in an amount sufiicient to inhibit said layer from becoming discolored.

8. A photographic color element as defined in claim 7 wherein said amino acid is glycine,

9. A photographic color element as defined in claim 7 wherein said amino acid is glycylglycine.

10. A photographic color element as defined in claim 7 wherein said amino acid is N,N-diethylglycine.

References Cited by the Examiner UNITED STATES PATENTS 2,356,486 8/1944 Weissberger et al 9656 2,440,954 5/1948 Jennings a 9656 2,618,559 11/1952 Gunther et al 96-56 3,201,243 8/1965 Larson 96-56 NORMAN G. TORCHIN, Primary Examiner. 

1. THE METHOD OF INHIBITING THE DISCOLORATION OF A WATER-PERMEABLE PHOTOGRAPHIC LAYER CONTAINING A COLOR IMAGE, SAID LAYER BEING SUBSTANTIALLY FREE OF DEVELOPED SILVER AND RESIDUAL SILVER HALIDE, WHICH COMPRISES IMBIBING IN SAID LAYER AN AQUEOUS SOLUTION OF AN AMINO ACID SELECTED FROM THE CLASS CONSISTING OF GLYCINE, B-ALANINE, BETAINE, AN ALKYGLYCINE IN WHICH THE ALKYL GROUP HAS FROM 1 TO 6 CARBON ATOMS, AND DIPEPTIDES OF THE SAID ACIDS. 